The present invention relates to a semiconductor manufacturing apparatus and, more particularly, to a CVD apparatus used to grow a silicon oxide film, and a method of cleaning the interior of the CVD apparatus.
CVD (Chemical Vapor Deposition) techniques include thermal CVD, plasma CVD, and photo assisted CVD techniques. A CVD apparatus is one of semiconductor manufacturing apparatuses for growing, on a wafer, a thin SiO.sub.2 film and the like required to fabricate a semiconductor element. In the CVD apparatus, as the thin SiO.sub.2 film is growing on the wafer, a perfect or imperfect oxide film mainly consisting of Si and O attaches to and is deposited on the inner wall surface of a reaction chamber (to be referred to as a chamber hereinafter), an insulator surface, a susceptor or electrode portion, a vacuum seal portion, a window plate, and the like. With increases in thicknesses, these films peel off to attach as particles to the wafer, resulting in a malfunction of the semiconductor element.
For this reason, the interior of the chamber is cleaned at a predetermined period, e.g., when an unnecessary film like the one described above is deposited to several .mu.m in the chamber. This cleaning step has conventionally been performed in any one of the following three ways.
(a) The chamber is disassembled and washed. That is, the disassembled chamber is dipped in a processing solution such as aqua regia for a predetermined period of time. PA1 (b) Plasma cleaning using CF.sub.4, C.sub.2 F.sub.6, or NF.sub.3 PA1 (c) Plasmaless cleaning using ClF.sub.3 or F.sub.2 PA1 (1) Cleaning PA1 (2) Pre-coating PA1 (3) Film formation on the wafer (actual manufacturing process) PA1 (a) As described above, the cleaning rate changes in and out of the plasma region. At a portion where the cleaning rate is high, the inner chamber wall is exposed early and damaged by the plasma. The damage in the CVD apparatus may become a new cause of generation of particles. Further, consumables inside the apparatus must be frequently exchanged, resulting in a very high cost. PA1 (b) To simultaneously remove the pre-coated film on the inner chamber wall leads to a long cleaning time. In addition, since the protection film must be formed again in the pre-coating step, the total processing time is prolonged due to the time required to perform the pre-coating step. PA1 (1) There is provided a method of cleaning a CVD apparatus at a high speed. PA1 (2) There is provided a method of selectively cleaning only a desired portion while suppressing corrosion (etching) of the interior of the CVD apparatus and preventing generation of particles. PA1 (3) There is provided a method of controlling the cleaning time and a cleaning portion in cleaning the CVD apparatus, and eliminating the pre-coating step in the cleaned chamber. PA1 (4) There is provided a method of generating a cleaning gas to be actually used for cleaning inside the CVD apparatus in cleaning the CVD apparatus, and cleaning the CVD apparatus with the generated gas. PA1 (5) There is provided a semiconductor manufacturing apparatus cleaning method which realizes a low manufacturing cost and a short processing time without generating any particle by selectively removing only a film deposited on a pre-coated film formed in the pre-coating step in cleaning the CVD apparatus. PA1 (6) There is provided a CVD apparatus which realizes the above cleaning methods (1) to (5).
Since processing (a) is the same as overhaul processing, it requires a long-time work, decreasing the availability of the CVD apparatus. Processing (b), which is a method of cleaning an unnecessary SiO.sub.2 film in the chamber without disassembling the chamber, has a low cleaning rate. The cleaning rate means the etching rate of SiO.sub.2 and is about 100 to 300 nm/min, so that the throughput (manufacturing efficiency) of the CVD apparatus lowers.
Since the cleaning (etching) effect of plasma cleaning (b) is low out of the plasma region, the cleaning rate decreases on the inner chamber wall and the insulator surface corresponding to the peripheral region of the plasma. Further, an O-ring (vacuum seal portion coupled to the window plate) in and near the plasma may be undesirably corroded to generate particles.
Plasma cleaning (c) has fewer limitations on cleaning portions than plasma cleaning (b), but its cleaning rate is as low as 100 nm/min or lower. In addition, the O-ring and the like are corroded to generate particles.
A thermal oxide SiO.sub.2 film, and an SiO.sub.2 film formed by CVD at a reduced or atmospheric pressure using a source gas of silane, tetraethoxysilane (TEOS), or the like are mainly used to manufacture a semiconductor device. Particularly, the SiO.sub.2 film formed by plasma CVD is used to insulate aluminum (Al) interconnections because this film is formed at a low temperature of about 400.degree. C.
In recent years, along with a higher integration and higher speed of semiconductor elements, the presence of contaminants contained in the SiO.sub.2 film and particles poses serious problems due to the following reasons. When the SiO.sub.2 film is formed on the semiconductor substrate using the plasma, stainless steel and aluminum members as constituent elements of the chamber become a metal contamination source and are doped in the SiO.sub.2 film on the semiconductor substrate after the interior of the chamber is exposed to the plasma, or the SiO.sub.2 film deposited on the inner chamber wall and the like peels off.
A current measure is a method of forming an SiO.sub.2 film in advance as a protection film on the inner chamber wall (pre-coating step) before forming an SiO.sub.2 film on a semiconductor substrate, and then loading the semiconductor substrate into the chamber.
More specifically, the semiconductor substrate is loaded into the chamber after the pre-coating step, and a desired thin film is formed on the semiconductor substrate. Thereafter, the semiconductor substrate is unloaded from the chamber. Alternatively, loading, thin film formation, and unloading of a plurality of number of semiconductor substrates are repeatedly executed after the pre-coating step. In this case, it should be noted that the film deposited in the chamber causes generation of particles, as described above.
Plasma cleaning is generally performed in the plasma CVD apparatus using CF.sub.4 or the like for a long period of time. As described above, the step of pre-coating the inner chamber wall and the like with an SiO.sub.2 film about several ten nm to 1 .mu.m thick is performed prior to the step of growing a film on an actual wafer. This step is performed to prevent metal contamination of the SiO.sub.2 film on the wafer by the stainless steel and aluminum members in the chamber.
That is, to operate the CVD apparatus while decreasing particles as much as possible, as described above, the steps (1), (2), and (3) must be performed in this order, though not every operation.
In the plasma cleaning method, however, the protection film (pre-coated film) formed in advance in the pre-coating step is also removed when the film deposited in the chamber is removed. For this reason, this plasma cleaning method has the following problems (a) and (b).
Considering an increase in throughput of the CVD apparatus and a reduction in manufacturing cost, attention is given to the time associated with cleaning. To operate the CVD apparatus while decreasing particles as much as possible, as described above, (1) cleaning, (2) pre-coating, and (3) film formation on the wafer (actual manufacturing process) must be performed in this order, though not every operation. That is, since the pre-coating step is performed in addition to a long cleaning time, the throughput of the whole CVD apparatus decreases. Further, consumables inside the apparatus must be frequently exchanged due to a long cleaning time, resulting in a high manufacturing cost. Therefore, various measures must be adopted for cleaning.